.\" $XFree86$
'\" te
'\"! tbl|eqn | mmdoc
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 24 September 1999
.ds Re Release 1.2.1
.ds Dp Jan 14 18:30
.ds Dm 01 pixelstor
.ds Xs 12758 17 pixelstore.gl
.TH GLPIXELSTORE 3G
.SH NAME
.B "glPixelStoref, glPixelStorei
\- set pixel storage modes

.SH C SPECIFICATION
void \f3glPixelStoref\fP(
GLenum \fIpname\fP,
.nf
.ta \w'\f3void \fPglPixelStoref( 'u
	GLfloat \fIparam\fP )
.fi
void \f3glPixelStorei\fP(
GLenum \fIpname\fP,
.nf
.ta \w'\f3void \fPglPixelStorei( 'u
	GLint \fIparam\fP )
.fi

.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\f2pname\fP\ \ 'u 
\f2pname\fP
Specifies the symbolic name of the parameter to be set.
Six values affect the packing of pixel data into memory:
\%\f3GL_PACK_SWAP_BYTES\fP,
\%\f3GL_PACK_LSB_FIRST\fP,
\%\f3GL_PACK_ROW_LENGTH\fP,
\%\f3GL_PACK_IMAGE_HEIGHT\fP,
\%\f3GL_PACK_SKIP_PIXELS\fP, 
\%\f3GL_PACK_SKIP_ROWS\fP,
\%\f3GL_PACK_SKIP_IMAGES\fP, and
\%\f3GL_PACK_ALIGNMENT\fP.
Six more affect the unpacking of pixel data \f2from\fP memory:
\%\f3GL_UNPACK_SWAP_BYTES\fP,
\%\f3GL_UNPACK_LSB_FIRST\fP,
\%\f3GL_UNPACK_ROW_LENGTH\fP,
\%\f3GL_UNPACK_IMAGE_HEIGHT\fP,
\%\f3GL_UNPACK_SKIP_PIXELS\fP, 
\%\f3GL_UNPACK_SKIP_ROWS\fP, 
\%\f3GL_UNPACK_SKIP_IMAGES\fP, and
\%\f3GL_UNPACK_ALIGNMENT\fP.
.TP
\f2param\fP
Specifies the value that \f2pname\fP is set to.
.SH DESCRIPTION

\%\f3glPixelStore\fP sets pixel storage modes that affect the operation of subsequent
\%\f3glDrawPixels\fP and \%\f3glReadPixels\fP as well as the unpacking of
polygon stipple patterns (see \%\f3glPolygonStipple\fP), bitmaps (see
\%\f3glBitmap\fP), texture patterns (see \%\f3glTexImage1D\fP,
\%\f3glTexImage2D\fP, \%\f3glTexImage3D\fP, \%\f3glTexSubImage1D\fP,
\%\f3glTexSubImage2D\fP, \%\f3glTexSubImage3D\fP).
Additionally, if the \%\f3GL_ARB_imaging\fP extension is supported, pixle
storage modes affect convlution filters
(see \%\f3glConvolutionFilter1D\fP, \%\f3glConvolutionFilter2D\fP, and
\%\f3glSeparableFilter2D\fP, color table (see \%\f3glColorTable\fP, and 
\%\f3glColorSubTable\fP, and unpacking histogram (See \%\f3glHistogram\fP),
and minmax (See \%\f3glMinmax\fP) data.
.P
\f2pname\fP is a symbolic constant indicating the parameter to be set, and
\f2param\fP is the new value.  Six of the twelve storage parameters affect
how pixel data is returned to client memory.
They are as follows:
.TP 10
\%\f3GL_PACK_SWAP_BYTES\fP
If true,
byte ordering for multibyte color components,
depth components,
color indices,
or stencil indices
is reversed.
That is,
if a four-byte component consists of bytes
$b sub 0$,
$b sub 1$,
$b sub 2$,
$b sub 3$,
it is stored in memory as
$b sub 3$,
$b sub 2$,
$b sub 1$,
$b sub 0$
if \%\f3GL_PACK_SWAP_BYTES\fP is true.
\%\f3GL_PACK_SWAP_BYTES\fP has no effect on the memory order of components
within a pixel,
only on the order of bytes within components or indices.
For example,
the three components of a \%\f3GL_RGB\fP  pixel are always stored with
red first,
green second,
and blue third,
regardless of the value of \%\f3GL_PACK_SWAP_BYTES\fP.
.TP
\%\f3GL_PACK_LSB_FIRST\fP
If true,
bits are ordered within a byte from least significant to most significant;
otherwise,
the first bit in each byte is the most significant one.
This parameter is significant for bitmap data only.
.TP
\%\f3GL_PACK_ROW_LENGTH\fP
If greater than 0,
\%\f3GL_PACK_ROW_LENGTH\fP defines the number of pixels in a row.
If the first pixel of a row is placed at location $p$ in memory,
then the location of the first pixel of the next row is obtained by skipping
.sp
.ce
$k ~=~~ left  { ^ lpile { n l above {a over s left ceiling { s n l } over a right ceiling}} ~~ lpile {s ~>=~ a above s ~<~ a }$
.sp
components or indices,
where $n$ is the number of components or indices in a pixel,
$l$ is the number of pixels in a row
(\%\f3GL_PACK_ROW_LENGTH\fP if it is greater than 0,
the $width$ argument to the pixel routine otherwise),
$a$ is the value of \%\f3GL_PACK_ALIGNMENT\fP, and
$s$ is the size, in bytes, of a single component
(if $ a < s$, then it is as if $a ~=~ s$).
In the case of 1-bit values,
the location of the next row is obtained by skipping
.sp
.ce
$k ~=~ 8 a left ceiling { n l } over { 8 a } ^ right ceiling$
.sp
components or indices.
.IP
The word \f2component\fP in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage  \%\f3GL_RGB\fP,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
.TP
\%\f3GL_PACK_IMAGE_HEIGHT\fP
If greater than 0,
\%\f3GL_PACK_IMAGE_HEIGHT\fP defines the number of pixels in an image
three-dimensional texture volume.
Where ``image'' is defined by all pixels sharing the same third
dimension index.
If the first pixel of a row is placed at location $p$ in memory,
then the location of the first pixel of the next row is obtained by skipping
.sp
.ce
$k ~=~~ left  { ~ lpile { n l h above {a over s left ceiling { s n l h }
over a ^ right ceiling}} ~~ lpile {s ~>=~  a above s ~<~  a }$
.sp
components or indices, where $n$ is the number of components or indices
in a pixel, $l$ is the number of pixels in a row
(\%\f3GL_PACK_ROW_LENGTH\fP if it is greater than 0,  the
$width$ argument to \%\f3glTexImage3d\fP otherwise), $h$ is the number of
rows in a pixel image (\%\f3GL_PACK_IMAGE_HEIGHT\fP if it is greater than
0, the $height$ argument to the \%\f3glTexImage3D\fP routine otherwise),
$a$ is the value of
\%\f3GL_PACK_ALIGNMENT\fP, and $s$ is the size, in bytes, of a single
component (if $ a < s$, then it is as if $a = s$).
.IP
The word \f2component\fP in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage  \%\f3GL_RGB\fP,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
.TP
\%\f3GL_PACK_SKIP_PIXELS\fP, \%\f3GL_PACK_SKIP_ROWS\fP, and \%\f3GL_PACK_SKIP_IMAGES\fP
These values are provided as a convenience to the programmer;
they provide no functionality that cannot be duplicated simply by
incrementing the pointer passed to \%\f3glReadPixels\fP.
Setting \%\f3GL_PACK_SKIP_PIXELS\fP to $i$ is equivalent to incrementing
the pointer by $i n$ components or indices,
where $n$ is the number of components or indices in each pixel.
Setting \%\f3GL_PACK_SKIP_ROWS\fP to $j$ is equivalent to incrementing
the pointer by $j m$ components or indices,
where $m$ is the number of components or indices per row,
as just computed in the \%\f3GL_PACK_ROW_LENGTH\fP section.
Setting \%\f3GL_PACK_SKIP_IMAGES\fP to $k$ is equivalent to incrementing
the pointer by $k p$, where $p$ is the number of components or indices
per image, as computed in the \%\f3GL_PACK_IMAGE_HEIGHT\fP section.
.TP
\%\f3GL_PACK_ALIGNMENT\fP
Specifies the alignment requirements for the start of each pixel row in memory.
The allowable values are 
1 (byte-alignment),
2 (rows aligned to even-numbered bytes),
4 (word-alignment), and
8 (rows start on double-word boundaries).
.P
The other six of the twelve storage parameters affect how pixel data is
read from client memory.
These values are significant for \%\f3glDrawPixels\fP,
\%\f3glTexImage1D\fP,
\%\f3glTexImage2D\fP,
\%\f3glTexImage3D\fP,
\%\f3glTexSubImage1D\fP,
\%\f3glTexSubImage2D\fP,
\%\f3glTexSubImage3D\fP,
\%\f3glBitmap\fP, and
\%\f3glPolygonStipple\fP.
.P
Additionally, if the \%\f3GL_ARB_imaging\fP extension is supported,
\%\f3glColorTable\fP,
\%\f3glColorSubTable\fP,
\%\f3glConvolutionFilter1D\fP,
\%\f3glConvolutionFilter2D\fP, and
\%\f3glSeparableFilter2D\fP.
They are as follows:
.TP
\%\f3GL_UNPACK_SWAP_BYTES\fP
If true,
byte ordering for multibyte color components,
depth components,
color indices,
or stencil indices
is reversed.
That is,
if a four-byte component consists of bytes
$b sub 0$,
$b sub 1$,
$b sub 2$,
$b sub 3$,
it is taken from memory as
$b sub 3$,
$b sub 2$,
$b sub 1$,
$b sub 0$
if \%\f3GL_UNPACK_SWAP_BYTES\fP is true.
\%\f3GL_UNPACK_SWAP_BYTES\fP has no effect on the memory order of components
within a pixel,
only on the order of bytes within components or indices.
For example,
the three components of a \%\f3GL_RGB\fP  pixel are always stored with
red first,
green second,
and blue third,
regardless of the value of \%\f3GL_UNPACK_SWAP_BYTES\fP.
.TP
\%\f3GL_UNPACK_LSB_FIRST\fP
If true,
bits are ordered within a byte from least significant to most significant;
otherwise,
the first bit in each byte is the most significant one.
This is relevant only for bitmap data.
.TP
\%\f3GL_UNPACK_ROW_LENGTH\fP
If greater than 0,
\%\f3GL_UNPACK_ROW_LENGTH\fP defines the number of pixels in a row.
If the first pixel of a row is placed at location $p$ in memory,
then the location of the first pixel of the next row is obtained by skipping
.sp
.ce
$k ~=~~ left  { ~ lpile { n l above {a over s left ceiling { s n l }
over a ^ right ceiling}} ~~ lpile {s  ~>=~ a above s ~<~  a }$
.sp
components or indices,
where $n$ is the number of components or indices in a pixel,
$l$ is the number of pixels in a row
(\%\f3GL_UNPACK_ROW_LENGTH\fP if it is greater than 0,
the $width$ argument to the pixel routine otherwise),
$a$ is the value of \%\f3GL_UNPACK_ALIGNMENT\fP, and
$s$ is the size, in bytes, of a single component
(if $ a < s$, then it is as if $a = s$).
In the case of 1-bit values,
the location of the next row is obtained by skipping
.sp
.ce
$k ~=~ 8 a left ceiling { n l } over { 8 a } right ceiling$
.sp
components or indices.
.IP
The word \f2component\fP in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage  \%\f3GL_RGB\fP,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
.TP
\%\f3GL_UNPACK_IMAGE_HEIGHT\fP
If greater than 0,
\%\f3GL_UNPACK_IMAGE_HEIGHT\fP defines the number of pixels in an image of
a three-dimensional texture volume.  Where ``image'' is defined by all
pixel sharing the same third dimension index.
If the first pixel of a row is placed at location $p$ in memory,
then the location of the first pixel of the next row is obtained by skipping
.sp
.ce
$k ~=~~ left  {~ lpile { n l h above {a over s left ceiling { s n l h }
over a ^ right ceiling}} ~~ lpile {s ~ >=~  a above s  ~<~  a }$
.sp
components or indices,
where $n$ is the number of components or indices in a pixel,
$l$ is the number of pixels in a row
(\%\f3GL_UNPACK_ROW_LENGTH\fP if it is greater than 0,
the $width$ argument to \%\f3glTexImage3D\fP otherwise),
$h$ is the number of rows in an image (\%\f3GL_UNPACK_IMAGE_HEIGHT\fP if
it is greater than 0, the $height$ argument to \%\f3glTexImage3D\fP otherwise),
$a$ is the value of \%\f3GL_UNPACK_ALIGNMENT\fP, and
$s$ is the size, in bytes, of a single component
(if $ a < s$, then it is as if $a ~=~ s$).
.IP
The word \f2component\fP in this description refers to the nonindex values
red,
green,
blue,
alpha,
and depth.
Storage  \%\f3GL_RGB\fP,
for example,
has three components per pixel:
first red,
then green,
and finally blue.
.TP
\%\f3GL_UNPACK_SKIP_PIXELS\fP and \%\f3GL_UNPACK_SKIP_ROWS\fP
These values are provided as a convenience to the programmer;
they provide no functionality that cannot be duplicated by
incrementing the pointer passed to
\%\f3glDrawPixels\fP,
\%\f3glTexImage1D\fP,
\%\f3glTexImage2D\fP,
\%\f3glTexSubImage1D\fP,
\%\f3glTexSubImage2D\fP,
\%\f3glBitmap\fP, or
\%\f3glPolygonStipple\fP.
Setting \%\f3GL_UNPACK_SKIP_PIXELS\fP to $i$ is equivalent to incrementing
the pointer by $i n$ components or indices,
where $n$ is the number of components or indices in each pixel.
Setting \%\f3GL_UNPACK_SKIP_ROWS\fP to $j$ is equivalent to incrementing
the pointer by $j k$ components or indices,
where $k$ is the number of components or indices per row,
as just computed in the \%\f3GL_UNPACK_ROW_LENGTH\fP section.
.TP
\%\f3GL_UNPACK_ALIGNMENT\fP
Specifies the alignment requirements for the start of each pixel row in memory.
The allowable values are
1 (byte-alignment),
2 (rows aligned to even-numbered bytes),
4 (word-alignment), and
8 (rows start on double-word boundaries).
.P
The following table gives the type,
initial value,
and range of valid values for each storage parameter
that can be set with \%\f3glPixelStore\fP.
.sp

.TS
center tab(:) delim($$) ;
lb cb cb cb
l c c c.
_
\f2pname\fP:Type:Initial Value:Valid Range
_
\%\f3GL_PACK_SWAP_BYTES\fP:boolean:false:true or false
\%\f3GL_PACK_LSB_FIRST\fP:boolean:false:true or false
\%\f3GL_PACK_ROW_LENGTH\fP:integer:0:[0,\(if)
\%\f3GL_PACK_IMAGE_HEIGHT\fP:integer:0:[0, \(if)
\%\f3GL_PACK_SKIP_ROWS\fP:integer:0:[0,\(if)
\%\f3GL_PACK_SKIP_PIXELS\fP:integer:0:[0,\(if)
\%\f3GL_PACK_SKIP_IMAGES\fP:integer:0:[0,\(if)
\%\f3GL_PACK_ALIGNMENT\fP:integer:4:1, 2, 4, or 8
_
\%\f3GL_UNPACK_SWAP_BYTES\fP:boolean:false:true or false
\%\f3GL_UNPACK_LSB_FIRST\fP:boolean:false:true or false
\%\f3GL_UNPACK_ROW_LENGTH\fP:integer:0:[0,\(if)
\%\f3GL_UNPACK_IMAGE_HEIGHT\fP:integer:0:[0,\(if)
\%\f3GL_UNPACK_SKIP_ROWS\fP:integer:0:[0,\(if)
\%\f3GL_UNPACK_SKIP_PIXELS\fP:integer:0:[0,\(if)
\%\f3GL_UNPACK_SKIP_IMAGES\fP:integer:0:[0,\(if)
\%\f3GL_UNPACK_ALIGNMENT\fP:integer:4:1, 2, 4, or 8
_
.TE

.sp
\%\f3glPixelStoref\fP can be used to set any pixel store parameter.
If the parameter type is boolean,
then if \f2param\fP is 0,
the parameter is false;
otherwise it is set to true.
If \f2pname\fP is a integer type parameter,
\f2param\fP is rounded to the nearest integer.
.P
Likewise, \%\f3glPixelStorei\fP can also be used to set any of the
pixel store parameters.
Boolean parameters are set to false if \f2param\fP is 0 and true otherwise.
.SH NOTES
The pixel storage modes in effect when
\%\f3glDrawPixels\fP,
\%\f3glReadPixels\fP,
\%\f3glTexImage1D\fP,
\%\f3glTexImage2D\fP,
\%\f3glTexImage3D\fP,
\%\f3glTexSubImage1D\fP,
\%\f3glTexSubImage2D\fP,
\%\f3glTexSubImage3D\fP,
\%\f3glBitmap\fP,
or \%\f3glPolygonStipple\fP is placed in a display list control the interpretation
of memory data.
Likewise, if the \%\f3GL_ARB_imaging\fP extension is supported, the pixel
storage modes in effect when
\%\f3glColorTable\fP,
\%\f3glColorSubTable\fP,
\%\f3glConvolutionFilter1D\fP,
\%\f3glConvolutionFilter2D\fP, of
\%\f3glSeparableFilter2D\fP is placed in a display list control the
interpretation of memory data.
The pixel storage modes in effect when a display list is executed are
not significant.
.P
Pixel storage modes are client state and must be pushed and restored
using 
.br
\%\f3glPushClientAttrib\fP and \%\f3glPopClientAttrib\fP.
.SH ERRORS
\%\f3GL_INVALID_ENUM\fP is generated if \f2pname\fP is not an accepted value.
.P
\%\f3GL_INVALID_VALUE\fP is generated if a negative row length,
pixel skip,
or row skip value is specified,
or if alignment is specified as other than 1, 2, 4, or 8.
.P
\%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glPixelStore\fP
is executed between the execution of \%\f3glBegin\fP
and the corresponding execution of \%\f3glEnd\fP.
.SH ASSOCIATED GETS
\%\f3glGet\fP with argument \%\f3GL_PACK_SWAP_BYTES\fP
.br
\%\f3glGet\fP with argument \%\f3GL_PACK_LSB_FIRST\fP
.br
\%\f3glGet\fP with argument \%\f3GL_PACK_ROW_LENGTH\fP
.br
\%\f3glGet\fP with argument \%\f3GL_PACK_IMAGE_HEIGHT\fP
.br
\%\f3glGet\fP with argument \%\f3GL_PACK_SKIP_ROWS\fP
.br
\%\f3glGet\fP with argument \%\f3GL_PACK_SKIP_PIXELS\fP
.br
\%\f3glGet\fP with argument \%\f3GL_PACK_SKIP_IMAGES\fP
.br
\%\f3glGet\fP with argument \%\f3GL_PACK_ALIGNMENT\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_SWAP_BYTES\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_LSB_FIRST\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_ROW_LENGTH\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_IMAGE_HEIGHT\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_SKIP_ROWS\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_SKIP_PIXELS\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_SKIP_IMAGES\fP
.br
\%\f3glGet\fP with argument \%\f3GL_UNPACK_ALIGNMENT\fP
.SH SEE ALSO
\%\f3glBitmap(3G)\fP,
\%\f3glColorTable(3G)\fP,
\%\f3glColorSubTable(3G)\fP,
\%\f3glConvolutionFilter1D(3G)\fP,
\%\f3glConvolutionFilter2D(3G)\fP,
\%\f3glSeparableFilter2D(3G)\fP,
\%\f3glDrawPixels(3G)\fP,
\%\f3glHistogram(3G)\fP,
\%\f3glMinmax(3G)\fP,
\%\f3glPixelMap(3G)\fP,
\%\f3glPixelTransfer(3G)\fP,
\%\f3glPixelZoom(3G)\fP,
\%\f3glPolygonStipple(3G)\fP,
\%\f3glPushClientAttrib(3G)\fP,
\%\f3glReadPixels(3G)\fP,
\%\f3glTexImage1D(3G)\fP,
\%\f3glTexImage2D(3G)\fP,
\%\f3glTexImage3D(3G)\fP,
\%\f3glTexSubImage1D(3G)\fP,
\%\f3glTexSubImage2D(3G)\fP,
\%\f3glTexSubImage3D(3G)\fP
